Re: [PATCH] crypto_user: Fix out-of-bounds read

Andy Lutomirski
2014-04-23T15:48:59Z

On Apr 23, 2014 4:40 AM, "Dan Carpenter" <dan.carpenter@oracle.com> wrote:
>
> On Tue, Apr 22, 2014 at 12:30:28PM -0700, Andy Lutomirski wrote:
> > This is unlikely to be exploitable for anything except an OOPS.
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Andy Lutomirski <luto@amacapital.net>
> > ---
> >
> > Notes:
> > This is entirely untested, but it looks obviously correct to me.
> >
> > crypto/crypto_user.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/crypto/crypto_user.c b/crypto/crypto_user.c
> > index 1512e41..bc7c4b5 100644
> > --- a/crypto/crypto_user.c
> > +++ b/crypto/crypto_user.c
> > @@ -460,7 +460,7 @@ static int crypto_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> > int type, err;
> >
> > type = nlh->nlmsg_type;
> > - if (type > CRYPTO_MSG_MAX)
> > + if (type < CRYPTO_MSG_BASE || type > CRYPTO_MSG_MAX)
> > return -EINVAL;
>
> Adding a check here is obviously harmless but I think this is only
> called from netlink_rcv_skb() which already checks:
>
> if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
> goto ack;
>
> NLMSG_MIN_TYPE is 0x10 as well, so I don't think we can hit your
> condition.
>
> Your patch freaked me out a little because this is one of the bugs that
> I should have caught throught static analysis.

BUILD_BUG_ON(NLMSG_MIN_TYPE != CRYPTO_MSG_BASE) might be a better
thing to add, then.

I don't feel so bad for missing this.

>
> regards,
> dan carpenter
>